This invention is related to a m-Menthenone, and to a general process for the synthesis of certain cyclohex-3-en-1-ones.
As is well known, terpenes, in general, have long been recognized as odoriferous components in fragrance compositions. Because of their great importance to the fragrance industry, monoterpenes having a basic molecular formula of C.sub.10 H.sub.16 have been extensively studied, and numerous such terpenes and their alcohol, ketone aldehyde, and esters derivatives dot the scientific literature. Shown in Table I are representative examples of cyclohexenones, together with their publication citations, which are most pertinent to the present invention.
Table I discloses that Kraus and Zartner have synthesized the compound 2-methyl-4-isopropylcyclohex-3-en-1-one (MICO), based on instrumental data from NMR performed in carbon tetrachloride at 6 Hz (which shows a nine hydrogen doublet at tau=8.98 (J = 6 Hz) and a single hydrogen multiplet at tau=4.30), a mass spectrum (which shows a peak for the molecular ion at 152) and an infrared spectrum (which shows a carbonyl peak at 1750 reciprocal centimeters and an ethylenic unsaturation peak at 1645 reciprocal centimeters).
TABLE I ______________________________________ REPRESENTATIVE CYCLOHEXENONES Structural Formula Reference ______________________________________ ##STR1## U.S. Pat. No. 2,918,495 to Booth ##STR2## Beilstein, "Handbuch Der Organischen Chemie,"Vol. VIII, & III p. 256 ##STR3## Stork, et. al., J. Am. Chem. Soc., 85, 207, (1963). ##STR4## Huang, et. al., J. Am. Chem. Soc., 95, 1936-44 (1973); C.A. 78:135394n. Konst, et. al., Int. Flavours and Food Addit., 6 (2), 121 (1975). ##STR5## U.S. Pat. No. 3,397,120 to Diana et. al. ##STR6## U.S. Pat. No. 2,619,504 to Bibb, et. al. ##STR7## U.S. Pat. No. 2,887,479 to Heseltine U.S. Pat. No. 3,560,571 to Kropp ##STR8## U.S. Pat. No. 3,538,164 to Leffingwell, et. al. ##STR9## Gloor, et. al., Helv. Chim. Acta, 1974, 57(6), 1815-45; C.A. 82:24283p ##STR10## Zimmerman, et. al., J. Am. Chem. Soc., 97, 5497-5507, (1975); C.A. 83:163382d ##STR11## Villorelli, et al., Helv. Chim. Acta, 1975, 58(5), 1379-425; C.A. 84:583036 ##STR12## Ficini, et. al., Tetrahedron Lett., 1976, (9), 679-82; C.A. 85:204755 ##STR13## Kraus and Zartner, Tetrahedron Lett., 1977 (1), 13-16; G. Zartner, Dissertation, Universitat Tubingen, ______________________________________ 1975.
U.S. Pat. No. 3,538,164 to Leffingwell discloses that limonene 1,2-epoxide produces dihydrocarvone when treated with perchloric acid in an inert solvent, and that dihydrocarvone readily isomerizes to p-menth-3-en-2-one, according to the following reaction: ##STR14##
U.S. Pat. No. 3,560,571 to Kropp teaches that 3,4-epoxycarane (synthesized from 3-carene and a peracid) produces 4-caranone and p-menth-3-en-2-one when treated with Lewis acids such as zinc salts in a reaction medium such as benzene, according to the following reaction: ##STR15##
U.S. Pat. No. 3,814,733 to Bledsoe, et al., discloses that 2,3-epoxycarane (1) rearranges to 1-methyl-(1-methylethenyl)-cyclohex-2-en-1-ol (2) when treated with metatitanic acid, i.e., ##STR16##
It has also been reported (Ohloff and Giersch, Helv. Chim. Acta, 51, 1328 (1968) that epoxidation of 2,3-carene with peracetic acid leads directly, after saponification of acetates, to 1-methyl-4-(1-methylethenyl)-cyclohex-2-en-1-ol (2) and its hydrated derivative (3), i.e., ##STR17## Recent work by Arata, et al., (Tetrahedron Lett., 1976, 3861) has yielded findings, consistent with earlier results, showing that 2,3-epoxycarane undergoes rearrangement to the same 1-methyl-4(1-methylethenyl)-cyclohex-2-en-1-ol, and alcohols and hydrocarbons derived most likely therefrom, when reacted in the presence of solid acids and bases such as SiO.sub.2 -Al.sub.2 O.sub.3, Al.sub.2 O.sub.3, FeSO.sub.4, TiO.sub.2 -ZrO.sub.2 and CaO. Conversely, however, Arata, et al., found that 3,4-epoxycarane (4) gave relatively good yields of a ring contraction product, aldehyde (5) (along with ketones and allylic alcohols, almost all of which could be derived from an intermediate of type 6), when treated with the same solid acids and bases, according to the following reaction: ##STR18## Findings by Joshi, et al. (Tetrahedron, 27, 475 (1971)) and Settine, et al., (J. Org. Chem., 32, 2910 (1967)) have shown that such ring contraction products are also produced by ZnBr.sub.2 catalysis of the 3,4-epoxycarane rearrangment.
Finally, Arbuzov, et al. (Doklady Akademii Nauk SSSR, 204(5), 1115-1117 (1972)) have published that 2,3-epoxycarane, when isomerized with zinc bromide in benzene, yields the following: ##STR19##
Thus, while it would be desirable to be able to obtain 2-methyl-4-isopropylcyclohex-3-en-1-one (MICO) or its alkyl substituted derivatives from 2,3-epoxycarane by a single step synthetic route, no such teaching may be found in the prior art.